Certain embodiments of the present invention are directed to integrated circuits. More particularly, some embodiments of the invention provide systems and methods for output regulation. Merely by way of example, some embodiments of the invention have been applied to amplification systems. But it would be recognized that the invention has a much broader range of applicability.
FIG. 1 is a simplified conventional diagram showing an amplification system using a Class-D amplifier with one channel. The amplification system 100 includes a modulator 102, an output stage 104, a low-pass filter 106, and an output load 116. The modulator 102 includes an oscillator 108, a comparator 110 and a loop filter 112. For example, the output load 116 is a speaker. In another example, the modulator 102, the output stage 104, and the low-pass filter 106 are included in a Class-D amplifier. In yet another example, the low-pass filter 106 includes one or more inductors and/or one or more capacitors. In yet another example, the low-pass filter 106 includes one or more bead cores and/or one or more capacitors.
The loop filter 112 receives an input audio signal 118 and an output signal 120 (e.g., a pulse-width-modulation signal) and outputs a filtered signal 122 to the comparator 110. For example, the input audio signal 118 includes a pair of input signals. The oscillator 108 generates a clock signal 126 and a ramp signal 124 which is received by the comparator 110. The comparator 110 outputs a comparison signal 128 that indicates a comparison between the ramp signal 124 and the filtered signal 122. The output stage 104 receives the comparison signal 128 and generates the output signal 120. The low-pass filter 106 converts the output signal 120 to an audio signal 130 to drive the load 116. As shown in FIG. 1, one channel including the modulator 102 and the output stage 104 is implemented. Multiple channels may be used for audio-amplification applications.
In one embodiment, the loop filter 112 amplifies an error signal between the input signal 118 and a feedback signal associated with the output signal 120. For example, the loop filter 112 includes a low pass filter which has a very high gain (e.g., a high gain larger than 1000) in a low frequency range and a very low gain (e.g., a low gain much smaller than 1) in a high frequency range. In another example, if a signal includes a low-frequency component and a high-frequency component, the loop filter 112 amplifies the low-frequency component with a high gain and amplifies the high-frequency component with a low gain (e.g., a low gain much smaller than 1). In yet another example, if the high-frequency component is close to a switching frequency of the amplification system 100, the loop filter 112 attenuates the high-frequency component. In one embodiment, the loop filter 112 includes one or more stages of analog integrators.
FIG. 2 is a simplified conventional diagram for an amplification system with multiple channels. The amplification system 300 includes multiple channels 2021, . . . , 202n, . . . , 202N, where N2 and 1nN. The first channel 2021 includes a loop filter 2041, comparators 2061 and 2081, a logic controller 2101, driving components 2121 and 2141, transistors 2161, 2181, 2201 and 2221, and a low-pass filter 2241. The logic controller 2101 includes one or more buffers. For example, the low-pass filter 2241 includes one or more inductors and/or one or more capacitors. In another example, the low-pass filter 2241 includes one or more bead cores and/or one or more capacitors. Other channels have similar components as the first channel. As shown in FIG. 2, these channels 2021, . . . , 202n, . . . , 202N share a common ramp signal 228 and generate output signals (e.g., 2341, . . . , 234n, . . . , 234N and/or 2361, . . . , 236n, . . . , 236N) so that audio signals are provided to output loads 2221, . . . , 222n, . . . , 222N (e.g., speakers) respectively.
In one embodiment, the loop filter 2041 amplifies the error signal between an input differential signal and a feedback differential signal associated with an output differential signal. The input differential signal represents a difference between the input signals 2301 and 2321, and the output differential signal represents a difference between the output signals 2341 and 2361. For example, the loop filter 2041 is a low pass filter and it has a very high gain (e.g., a high gain that is greater than 1000) in a low frequency range and a very low gain (e.g., a low gain that is much smaller than 1) in a high frequency range. In another example, if a signal includes a low-frequency component and a high-frequency component, the loop filter 2041 amplifies the low-frequency component with a high gain and amplifies the high-frequency component with a low gain (e.g., a low gain that is much smaller than 1). In yet another example, if the high-frequency component is close to a switching frequency of the amplification system 200, the loop filter 2041 attenuates the high-frequency component. In one embodiment, the loop filter 2041 includes one or more stages of analog integrators. In some embodiments, loop filters in other channels are the same as the loop filter 2041.
FIG. 3 is a simplified conventional diagram for an amplification system including two channels. The amplification system 1700 includes two channels 17021 and 17022. The first channel 17021 includes a loop filter 17041, comparators 17061 and 17081, a logic controller 17101, driving components 17121 and 17141, transistors 17161, 17181, 17201 and 17221, and a low-pass filter 17241. The logic controller 17101 includes one or more buffers. For example, the low-pass filter 17241 includes one or more inductors and/or one or more capacitors. In another example, the low-pass filter 17241 includes one or more bead cores and/or one or more capacitors. The second channel 17022 has similar components as the first channel. As shown in FIG. 3, the two channels 17021 and 17022 share a common ramp signal 1728 and generate output signals (e.g., 17341, 17342 and/or 17361, 17362) so that audio signals are provided to output loads 17221 and 17222 (e.g., speakers) respectively.
For example, the loop filter 17041 amplifies the error signal between an input differential signal and a feedback differential signal associated with an output differential signal. The input differential signal represents a difference between the input signals 17301 and 17321, and the output differential signal represents a difference between the output signals 17341 and 17361. For example, the loop filter 17041 is a low pass filter and it has a very high gain (e.g., a high gain that is greater than 1000) in a low frequency range and a very low gain (e.g., a low gain that is much smaller than 1) in a high frequency range. In another example, if a signal includes a low-frequency component and a high-frequency component, the loop filter 17041 amplifies the low-frequency component with a high gain and amplifies the high-frequency component with a low gain (e.g., a low gain that is much smaller than 1). In yet another example, if the high-frequency component is close to a switching frequency of the amplification system 1700, the loop filter 17041 attenuates the high-frequency component. In one embodiment, the loop filter 17041 includes one or more stages of analog integrators. In some embodiments, the loop filter 17042 is the same as the loop filter 17041.
FIG. 4(a) is a simplified conventional timing diagram for the amplification system 1700 if the input differential signals of the channels 17021 and 17022 are both equal to zero volt. The waveform 2802 represents the input differential signal of the channel 17021 as a function of time, the waveform 2804 represents the output signal 17361 as a function of time, the waveform 2806 represents the output signal 17341 as a function of time, the waveform 2808 represents the input differential signal of the channel 17022 as a function of time, the waveform 2810 represents the output signal 17362 as a function of time, and the waveform 2812 represents the output signal 17342 as a function of time. For example, the input differential signals of the channels 17021 and 17022 being both equal to zero volt indicate that the input signals 17301 and 17321 are the same and the input signals 17302 and 17322 are the same.
FIG. 4(b) is a simplified conventional timing diagram for the amplification system 1700 if the input differential signals of the channels 17021 and 17022 are the same and both higher than zero volt. The waveform 2820 represents the input differential signal of the channel 17021 as a function of time, the waveform 2822 represents the output signal 17361 as a function of time, the waveform 2824 represents the output signal 17341 as a function of time, the waveform 2826 represents the input differential signal of the channel 17022 as a function of time, the waveform 2828 represents the output signal 17362 as a function of time, and the waveform 2829 represents the output signal 17342 as a function of time. For example, the input differential signal of the channel 17021 being higher than zero volt indicate that the input signal 17301 is higher than the input signal 17321. In another example, the input differential signal of the channel 17022 being higher than zero volt indicate that the input signal 17302 is higher than the input signal 17322.
FIG. 4(c) is a simplified conventional timing diagram for the amplification system 1700 if the input differential signals of the channels 17021 and 17022 are the same and both lower than zero volt. The waveform 2830 represents the input differential signal of the channel 17021 as a function of time, the waveform 2832 represents the output signal 17361 as a function of time, the waveform 2834 represents the output signal 17341 as a function of time, the waveform 2836 represents the input differential signal of the channel 17022 as a function of time, the waveform 2838 represents the output signal 17362 as a function of time, and the waveform 2840 represents the output signal 17342 as a function of time. For example, the input differential signal of the channel 17021 being lower than zero volt indicate that the input signal 17301 is lower than the input signal 17321. In another example, the input differential signal of the channel 17022 being lower than zero volt indicate that the input signal 17302 is lower than the input signal 17322.
As shown in FIG. 4(a), FIG. 4(b), and/or FIG. 4(c), in response to the same input differential signals for both the channels 17021 and 17022, the output signals 17341 and 17342 have approximately same phases, and the output signals 17361 and 17362 have approximately same phases.
The amplification systems 100, 200, and 1700 often have certain disadvantages. Hence it is highly desirable to improve such amplification systems.